Why BMI Thresholds Are Different for South Asians

Body Mass Index — weight in kilograms divided by height in metres squared — was standardised by the World Health Organization using data drawn mostly from European populations. The cut-offs it produced (underweight below 18.5, healthy 18.5–24.9, overweight 25–29.9, obese 30 and above) work reasonably well for the population they were built from.

They work less well for South Asians. At the same BMI, South Asian adults tend to carry a higher percentage of body fat — and more of it around the abdomen — than European adults of the same height and weight. This pattern is sometimes called the "thin-fat" phenotype: a BMI that reads as "healthy" can still carry meaningfully elevated risk.

Abdominal and visceral fat — the fat around the organs, not just under the skin — is more strongly linked to insulin resistance, type 2 diabetes and cardiovascular disease than overall body fat is. Population studies have repeatedly found South Asians developing type 2 diabetes and heart disease at BMI levels the standard scale would still call "normal" or only mildly overweight.

In response, the WHO convened an expert consultation specifically on BMI in Asian populations, and its findings led several national health bodies — including India's — to adopt narrower cut-offs for population screening.

These are the thresholds Calkut's BMI calculator uses when you switch on "South Asian thresholds" — and the same ones several South Asian national health guidelines use for screening:

The adjusted thresholds are most relevant if your recent ancestry traces to South Asia — India, Pakistan, Bangladesh, Sri Lanka, Nepal or the Maldives. Research on other Asian populations has produced broadly similar findings, though the exact cut-offs studied differ by region; Calkut's toggle is calibrated specifically to the South Asian data.

If none of this applies to you, the standard WHO thresholds remain the better default — which is why Calkut's calculator starts with them until you switch the toggle on.

BMI band is one input into how Calkut sets your calorie target, alongside your age, activity level and the pace you choose. Getting the band right matters: it changes which goals the app suggests and where it sets the safety floor on how aggressive a deficit it will let you pick.

You can turn South Asian thresholds on or off at any time, both in the calculator below and in your profile inside the app.

WHO Expert Consultation, "Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies," The Lancet, 2004.

World Health Organization Western Pacific Region and International Association for the Study of Obesity, "The Asia-Pacific Perspective: Redefining Obesity and its Treatment."